Preface Free

Principles of Brazing primarily aims at presenting the subject in a form that is readily accessible to practitioners of this joining technology, while at the same time offering a scientific perspective of brazing. It focuses on fundamental principles rather than providing recipes for producing brazed joints. Based on Principles of Soldering and Brazing, published in 1993, this volume includes much new material on brazing, covering progress over the past decade.

The largely artificial distinctions between brazing and soldering are preserved because, despite the many commonalities, it has been found that practicing engineers are concerned with either soldering or brazing and seldom are involved with both simultaneously. The companion volume, Principles of Soldering, addresses this complementary need. A large proportion of the literature on brazing and soldering may be charged with being heavy on description and light on critical analysis. We have endeavored to redress the balance, while striving to avoid being unduly simplistic or overly mathematical in our approach. Admittedly, we may not always have succeeded in this aim.

As in Principles of Soldering and Brazing, we have striven to maintain the focus on the fundamental aspects of brazing and have deliberately avoided entering into specific joining technologies in detail. Therefore, it is inevitable that some topics are not accorded due consideration, although it is hoped that sufficient references are provided to enable the reader to pursue these further.

The authors recognize that the range and extent of the knowledge base of metal joining is not immediately obvious, and mastery of the subject requires a fairly deep understanding of materials. This point is particularly apposite to the wetting of ceramics by metals, discussed in Chapter 7. The behavior of self-fluxing copper-phosphorus brazes and the poor mechanical integrity of joints made with these brazes to steel unless nickel is present represents another example of the interplay of factors that need to be considered and understood (see Chapter 3).

Two areas of brazing that have benefited from significant research efforts in recent years are active brazing and diffusion brazing. These are also areas in which the authors have been directly involved, and accordingly, individual chapters are devoted to each of these topics in this new edition (Chapters 6 and 7).

No attempt has been made to gather a comprehensive list of publications in our bibliography. Those that are included have been selected because they are useful basic texts, cover important subject matter, or relate to exemplary pieces of work, whether in respect of methodology, technique, or other noteworthy feature. It was felt that if the value of the book depended on its bibliography, it would rapidly become dated. The advent of computer search facilities and databases of scientific journal and conference abstracts should enable the reader who wishes to chase up references on specific topics to obtain further information without too much difficulty.

The reader should note that all compositions given in this book are expressed in weight percentage in accordance with the standard industrial practice, and these have, for the most part, been rounded to the nearest integer. The ratio of elements in intermetallic compounds, again by convention, refers to the atomic weight of the respective constituents. The general convention used for referring to braze alloy families is that adopted by the alloy phase diagram community, namely, in the alphabetical order of the elements, by chemical symbol. However, when referring to specific braze compositions, for the most part we have listed the elements in order of concentration. The alternative, which is widely accepted in the metal joining literature, is to express compositions in alphabetical order of the chemical symbols of the major constituents, followed by the minor constituents. The authors prefer the system based on concentration because, otherwise, lesser ingredients can punctuate the composition order, which would be illogical and avoids debate as to whether a constituent is a major or minor element. Thus, for example, we refer to an alloy of composition Ag-22Zn-21Cu-2Sn-0.01Ce as a silver-copper-zinc braze.

Specific references are given with each chapter. For those wishing to read more generally on particular topics, the authors recommend the texts listed in Appendix 2.

Many phase diagrams are subject to ongoing research, resulting in continued improvement in the accuracy and detail of the information. The most recent version of a diagram may be identified by consulting the latest cumulative index of phase diagrams, published in the Cumulative Index of the periodical Journal of Phase Equilibria (ASM International). This index refers to the source of the thermodynamically assessed diagram of interest. The reader is advised that the four compendia of binary phase diagrams published in the 1960s, 1970s, and 1980s (colloquially referred to as Hansen, Elliott, and Shunk) are now known to contain many errors and omissions.

Information on new developments in soldering and brazing is scattered throughout a wide range of periodicals, as reflected in the sources cited in the references appended to the individual chapters. To keep abreast of the literature, the authors have found especially useful the following abstract publications: Metals Abstracts and Science Abstracts. Technical libraries can provide automated searches against specified key words as a monthly service.

We wish to thank our many colleagues and ex-colleagues for their helpful advice and encouragement, particularly Chris Corti of the World Gold Council for sharing his insights into the brazing of jewelry.